[V8] The Old Gray Mare's hot flashes....

[Roger M. Woodbury]

I think I have found the problem that has been causing The Old Gray Mare to
have hot flashes.  If you didn't see the original thread, my "new" '90 Audi
100, aka, The Old Gray Mare, has been having hot flashes.  While driving
with the a/c on, periodically the cool air would turn warm, then after a few
minutes, would turn cool again.  

Normally this would take place on "temperate" days.  Days when the outside
temperature was in the seventies to low eighties.  On really intense bright
sunny days, with temperatures well into the eighties and above, the a/c
would blow cold without interruption.  

Last week while driving, I decided to turn off the a/c entirely, since it
really wasn't terribly warm.  I opened the sunroof, and cracked the driver's
window.  Turned the compressor off....selected "econ".  

AND.  Nothing.  Still warm air blowing out inside the car.

"Hmmmmmmmmmm," sez I.  "Very suspicious."  So here is my theory.

The "fault" is not in the a/c at all, and when the a/c is on, it is doing
what it is supposed to do, drive the air temp to what the temperature
selector says it is supposed to be.  

BUT, the heater control valve is vacuum operated.  (Either with or without
an electronic sensor...dunno which type yet).  And IF the heater control
valve is losing vacuum somewhere, then it could be allowing warm coolant to
run into the heater core, and provide heat AND a/c at the same time.
Depending on the temperature required by the air conditioner, it could be
overriding the cool air, until vacuum was restored.

First off, I will check the heater control valve this weekend.

Full report and pictures at eleven....uh...later when I have them.  Well,
maybe not pictures, but you get it.....

Roger

P.S.  I MAY be on the track of my "new" V8.  If the car is THE car, then I
think I will be permitted to buy it by the warden...ah, my wife, that is.
The pay off price will be a new Dyson vacuum which she really wants.  I
guess that's better than my first wife, who only seemed to be on a
broomstick....

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